(b) So now the program runs OK from the installed entry in the "Menu->Utility->General Utilities->Wish Binary Viewer".
Has a rather nice colorful [Orange] GUI!
Used it to "Open" the mbr.bin file and was given the kind of display I want [the code content as seen in the screenshots below].
Was then able to save a copy with a name specified by me.
Would it be possible to use a file-content-comparison program to display differences?